1. Field of the Invention
The present invention relates to a method for automatically varying the feed rate of a workpiece carriage in a numerically-controlled machine tool in the vicinity of permissible terminal positions for the carriage in the machine tool, and in particular to an improved method for varying the feed rate of a workpiece carriage in a computer-controlled nibbling machine which includes means for determining the position of the workpiece carriage.
2. Description of the Prior Art
Methods of the foregoing type for varying the feed rate of a workpiece carriage in a machine tool are known in the art. See, for example, Siemens AG catalog SINUMERIK 550C, dated October, 1974.
In machine tools in which the workpiece carriage is capable of reaching a high velocity and in which relatively heavy workpieces are operated upon, for example, nibbling machines, the feed rate must be reduced in the vicinity of the terminal positions of the workpiece carriage in order to prevent the occurrence of excessive stress and, in particular, to enable an emergency stop of the workpiece carriage to be effected in any situation. These objectives can theoretically be achieved by utilizing mechanical end switches mounted in the vicinity of the terminal positions of the workpiece carriage to reduce the velocity of the workpiece carriage when they are approached by the carriage. Considerable means are required, however, for the installation and adjustment of such switches. And it is likewise expensive to take into consideration the foregoing factors when programming the numerical control of such a machine tool.